Polycrystalline super hard materials, such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. They generally contain ultrahard abrasive particles dispersed in a second phase matrix. The matrix may be metallic or ceramic or a cermet. The ultrahard abrasive particles may be diamond, cubic boron nitride (cBN), silicon carbide or silicon nitride and the like. These particles may be bonded to each other during the high pressure and high temperature compact manufacturing process generally used, forming a polycrystalline mass, or may be bonded via the matrix of second phase material(s) to form a sintered polycrystalline body. Such bodies are generally known as polycrystalline diamond or polycrystalline cubic boron nitride, where they contain diamond or cBN as the ultrahard abrasive, respectively. Examples of diamond and cubic boron nitride abrasive compacts are described in U.S. Pat Nos. 3,745,623; 3,767,371; 3,743,489; 4,334,928; 5,466,642 and 5,328,875.
For example, U.S. Pat. No 4,334,928 teaches a sintered compact for use in a tool consisting essentially of 20 to 80 volume % of cubic boron nitride; and the balance being a matrix of at least one binder compound material selected from the group consisting of a carbide, a nitride, a carbonitride, a boride and a suicide of a IVa or a Va transition metal of the periodic table, mixtures thereof and their solid solution compounds. The matrix forms a continuous bonding structure in a sintered body with the high pressure boron nitride interspersed within a continuous matrix. The methods outlined in this patent all involve combining the desired materials using mechanical milling/mixing techniques such as ball milling, mortars and the like.
Sintered polycrystalline bodies may be ‘backed’ by forming them on a substrate. Cemented tungsten carbide, which may be used to form a suitable substrate, is formed from carbide particles dispersed, for example, in a cobalt matrix by mixing tungsten carbide particles/grains and cobalt together then heating to solidify. To form the cutting element with an ultra-hard material layer such as PCD or PCBN, diamond particles or grains or CBN grains are placed adjacent the cemented tungsten carbide body in a refractory metal enclosure such as a niobium enclosure and are subjected to high pressure and high temperature so that inter-grain bonding between the diamond grains or CBN grains occurs, forming a polycrystalline super hard diamond or polycrystalline CBN layer.
In some instances, the substrate may be fully cured prior to attachment to the ultra-hard material layer whereas in other cases, the substrate may be green (not fully cured). In the latter case, the substrate may fully cure during the HTHP sintering process. The substrate may be in powder form and may solidify during the sintering process used to sinter the ultra-hard material layer.
Polycrystalline super hard materials, such as polycrystalline diamond (PCD) and PCBN may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. A sintered polycrystalline body may be used as a tool insert to form an abrasive or cutting edge.
During a machining operation, tool inserts are susceptible to higher friction, which leads to increased flank wear, and higher temperatures, which lead to increased chemical wear, thereby shortening the tool life. The working life of tool inserts may be limited by fracture of the super hard material, including by spalling and chipping, or by wear of the tool insert. In many of these applications, the temperature of the superhard material may become elevated as it engages workpieces or other bodies. Mechanical properties of superhard material such as abrasion resistance, hardness and strength tend to deteriorate at elevated temperatures. In order to address this, a solid or liquid lubricant is provided during a machining operation (such as turning or milling) to reduce friction between the tool insert and the workpiece. FIG. 1 shows an example where a tool 1 comprises a tool insert 2. During a machining operation the tool insert 2 contacts a workpiece 3. Solid lubricant particles 4 are sprayed onto the cutting area to reduce friction between the tool insert 2 and the workpiece 3.